1. Field of the Invention
The present invention relates to the method and system to transmit layer 3 packets on an Asynchronous Transfer Mode (ATM) network.
2. Description of the Related Art
Currently, on the network where Internet Protocol (IP) is widely used on the Internet, each router needs to compare the destination address of all packets sent by the source host with an internal routing table, decide the route to transmit the packets (routing process), and transmit the packets. These conventional routers conduct this routing process for each packet of a flow comprising a series of packets, and as a result, the total quantity of the packets to be processed is accumulated, which causes a decrease in throughput and an increase in transmitting delay time.
As an example of solving the above problem, a layer 3 switching method IFMP (Ipsilon Flow Management Protocol in Internet Engineering Taskforce Request for Comment: IETF RFC1953) is used. In the case where a network is composed of a first ATM switch (here, sending) and a second ATM switch (here, receiving), for example, IFMP is implemented as follows:
1. Each ATM switch detects a flow by looking at the layer 3 packets which belong to the same flow and are received at the default Virtual Channel (VC);
2. The second ATM switch sends a flow redirect message using the default VC to the first ATM switch in order to lot it use a VC allocated for that flow as a dedicated VC;
3. The first ATM switch begins sending the packets of the flow using that dedicated VC; and
4. After both sides (source and destination) setup the dedicated VCs specially for that flow, the packets are transferred through the dedicated VCs between the source and destination ATM switches
However, the above-described IFMP has the following disadvantages.
1. The loads on each switch increase because each switch needs to have a flow detection function.
2. Redirection of flow on both source and destination ends needs to be completed before the switch can handle the flow. However, each switch will decide and request the flow-redirection to the source switch after it receives the first packet, which results in a long delay from the time when the first packet is received.
3. Because VPI and VCI will be allocated for each flow, the number of VPI and VCI Will become huge and the operation and administration of flow-redirection will be overload for switches.
An object of the present invention is to provide a method and system which can reduce a processing burden on each switch.
Another object of the present invention is to provide a method and system which can achieve the rapid flow switching of each switch.
According to the present invention, in a method for transferring a series of layer-3 packets received from a non-ATM network through an ATM network composed of a plurality of ATM switches, at an ingress gateway interfacing between the non-ATM network and the ATM network, the following stops are performed: a) determining whether a flow of the series of packets has been registered; b) determining a transfer route from a first packet of the series of packets according to a layer-3 routing protocol when the flow has not been registered; c) transmitting a connection setup message to a next-hop ATM switch of the ATM network according to the transfer route to ensure a connection dedicated to transfer of the series of packets; and d) transferring the series of packets received from the non-ATM network to the next-hop ATM switch through the connection after the connection has been set up.
At each of nodes receiving the connection setup message from an upstream node which is one of the ingress gateway and an adjacent ATM switch, the following steps are performed: determining a transfer route from the connection setup message according to a layer-3 routing protocol; transmitting a connection setup message to a next-hop node of the ATM network according to the transfer route to ensure a connection dedicated to transfer of the series of packets to the next-hop node; and transferring the series of packets received from the upstream node to the next-hop node through the connection after the connection has been set up.
At an ATM switch receiving the connection setup message, when the connection to the next-hop node is not set up yet, the series of packets are preferably transferred through a default connection to the next-hop node until the connection to the next-hop node has been set up.
Since the connection setup message is transmitted before a packet to be transferred on the layer 3 flow switching, the routing is allowed without assembling packets. The connection setup message is sent before actual packets arrive and the information conveyed by the connection setup message enables the routing of the actual packets. The actual packets will be transmitted on the allocated connection using hardware switching from the very first packet. Therefore, the processing of assembling packets can be removed and thereby the transfer delay is eliminated.
Further, there is no need to detect a flow on each switch. The ingress gateway is the only component that needs to detect the flow, and the switches on the way just need to recognize packets sent on the connection specified by the connection setup message as the flow. Therefore there is no need to detect the flow by looking at the port number and the line for each switch.